pdfSetPrintEmulatedMultiCopy

By default, the number of copies requested in a pdfPrint3 or
pdfStartPrintJob call is passed to the printer driver. But not
all printers/drivers support printing multiple copies and/or
collation. The pdfSetPrintEmulatedMultiCopy function can
be used to enable "emulated multi copy" mode, in which XpdfViewer will
generate a print stream with multiple copies (as specified by
the nCopies argument to pdfPrint3 or
pdfStartPrintJob) of each page, in collated order.

The advantage of emulated multi copy mode is that it will work on all
printers. The disadvantage is that the spool file will be larger
(because it contains multiple copies of each page).